If I buy an unlocked iphone in Singapore, will it work in the US?

[Masbro]

I'm travelling abroad for a few years, but reside in the US and want to purchase an unlocked iphone 6 or 7 in Singapore that will also work in the US (I'm already in Asia so won't be able to purchase in the US for a while). Are there particular specs I need to look for? Wondering how it works with US carriers when I get back home and want to use my phone for a couple months before I go abroad again. Thanks for your help.